1. Field of the Invention
The present invention relates to a suspension system having means for easily determining a change in the condition of a suspension which is caused by an external force applied to the suspension.
2. Description of the Relevant Art
There has been proposed a vehicular suspension system including a shock absorber having a coil spring with a lower end coupled to a knuckle by which a road wheel is rotatably supported and an upper end coupled to a vehicle body through a resilient member with an electrically conductive rubber layer mounted thereon as a strain detector (see Japanese Laid-Open Utility Model Publication No. 60-106807). While a motor vehicle equipped with such a suspension system is traveling, loads acting on the shock absorber and the resilient member are varied by irregularities on the road surface and swinging movement of the vehicle body, thus expanding and contracting the resilient member and the electrically conductive rubber member. Therefore, the road surface irregularities and the swinging movement of the vehicle body can be detected as changes in electric resistance which are brought about by the expansion and contraction of the rubber member.
Japanese Laid-Open Utility Model Publication No. 60-155610 discloses another vehicular suspension system including a shock absorber having a coil spring with a lower end coupled to a knuckle by which a road wheel is rotatably supported and an upper end coupled to a vehicle body through a resilient member. The upper end of the shock absorber and a load detector are fastened together to the vehicle body. The load detector comprises a piezoelectric element for producing an output signal indicative of a change in a load on the shock absorber.
Determination of a change in the condition of the suspension based on the detected value in the suspension assembly for controlling the attitude of the suspension lacks a desired degree of accuracy. Since the suspension system itself cannot detect a change in the height of the vehicle body from the ground as a change in the condition of the suspension which is induced by an external force applied, a separate vehicle height sensor is required. Because the known load detectors are mounted on the upper end of the shock absorber where a large load is concentrated, the suspension system is complex in structure, expensive to manufacture, and has a durability problem.